In virtually all industrial and municipal waste systems, waste water is laden with grit which must be removed from the water for proper processing and to protect downstream equipment. Grit removal systems such as grit extractors or grit traps have been used in many waste water treatment systems to remove grit from the waste water prior to passing the water onto further process and collect the grit to transfer to a recovery device of the system.
Grit removal systems operate according to a variety of methods. For example, some facilities hold grit-laden water in oversized storage tanks and allow the grit to settle out of the water over time. Other facilities use air induced flow patterns or forced vortex methods to separate grit from the water.
For example, one advantageous grit removal system includes an apparatus which includes flumes for injecting and extracting liquid (e.g., waste water) tangentially relative to a round chamber, thus creating a forced vortex in the chamber. The grit-laden waste water flows through a channel from an upstream portion of the waste water system and then into the round chamber of the grit removal system. Flow velocity into the round chamber facilitates operation of the grit removal system by creating a circular flow stream which causes the grit to settle near the bottom center of the round chamber. The grit in the input waste water is thus removed from the liquid stream and collected in the storage chamber for relatively easy removal. Such an apparatus is disclosed in U.S. Pat. No. 6,811,697 B2, the full disclosure of which is hereby incorporated by reference.
As another example, U.S. Pat. No. 4,767,532 (the full disclosure of which is hereby incorporated by reference) similarly discloses an apparatus for removing grit in which a grit storage chamber is provided beneath the center of the round chamber of the grit removal system. Liquid flow in the round chamber causes grit particles to settle toward the chamber floor, where they are urged radially inwardly so as to drop through an opening into a grit storage chamber.
U.S. Pat. Nos. 3,941,698 and 4,107,038 and U.S. Published Patent Application No. 2008/0105604 A1 also disclose grit extractor apparatuses. The disclosures of all of these patent documents are also hereby fully incorporated by reference.
Excellent grit removal systems are available, for example, from Smith & Loveless, Inc. of 14040 Santa Fe Trail Drive, Lenexa, Kans. 66215-1284, including its PISTA® grit removal system which has a flat bottomed grit chamber and operates on the forced vortex principal.
While those grit removal systems which use storage tanks remove grit based on retention time in the tanks, the more proactive grit removal systems (e.g., those relying on the vortex principal) operate most efficiently when the flow velocity of the waste water entering the system is within a design range. However, it should be appreciated that the flow of waste water into the channel to the round chamber may significantly vary. Moreover, it should be appreciated that since grit (including sand) in waste water does not float or flow consistently, if the velocity of flow is not sufficiently high the grit and sand may not be maintained in suspension and pushed down the channel, in which case it will settle to the bottom of a channel before reaching the grit removal system where it can be properly removed from the system.
In many areas, the flow rate of waste water may vary widely during a given day, as water use in the community and industry in the area, even if predictable, will seldom be uniform (e.g., a factory may discharge large amounts of waste water at different times of the day, and/or individual users may generate more load in the morning than at midnight).
Further, water usage may vary widely over the design life of a waste water system. For example, systems are often built to be able to handle a maximum load which may not be anticipated to occur for many years (e.g., when a new community is built out). Until that build out occurs, flow rates could be significantly less than designed for. Similarly, waste water systems built years ago to handle an anticipated maximum load may now find that the maximum load anticipated years ago will never occur (e.g., because planned buildings were never built, and/or home and industry usage became more efficient than was anticipated when the waste system was built).
Given these flow variations and a desire to minimize such variations in the flow velocity in the input channel and into the grit removal systems, attempts have been made to modify the rate.
For example, the input channels are generally formed of concrete with vertical side walls and flat bottoms, and where the flow velocity through such a channel (which is based on the actual flow rate of waste water at a given facility) has been found to be of an insufficient volume, concrete blocks or a vertical steel plate (fastened in place) have been placed in the channel to create a different vertical side wall which narrows the channel and thereby increases the flow velocity through the channel.
Additionally, baffles have been included in the grit removal system to direct waste water flow through the system so as to facilitate the desired vortex flow, such as shown in U.S. Pat. No. 6,811,697 B2. However, even with such improvements, a low flow volume in the input channel may result in a low velocity within the channel itself. As mentioned, insufficient flow velocity in the input channel can result in grit settling and accumulating in the channel rather than enter the grit removal system and be removed, in which case the settled grit will not be handled and removed by the system, but instead will undesirably accumulate in the channel and detrimentally effect the operational performance of the unit.
In short, it has heretofore been desirable, but difficult, to maintain the waste water flow velocity in the channels discharging into a grit removal system operating on the vortex principal within a design range. As a result, not only have such grit removal systems potentially been caused to operate inefficiently, but grit has also separated from the fluid at locations where the grit is not intended to be handled (e.g., in the input channel) and thus has undesirably accumulated at such locations.
The present invention is directed toward overcoming one or more of the problems set forth above.